The use of deinked waste paper as a fiber component constitutes prior art in the manufacture of newsprint, copy papers, sanitary papers and board.
The object of the present invention is also the use of deinking substances for high-grade printing papers such as, for instance, coating base papers, LWC and SC papers (rotogravure and offset printing). For these cases of use, both a high degree of cleanness as well as a high degree of whiteness is necessary. If it is possible to produce deinked materials of the required quality, the demand will be correspondingly high, i.e. desired clean types of waste paper will not be available in sufficient quantity. It will then be necessary to have recourse to so-called "household collected waste" consisting of about 40 to 60% old newspapers and 60 to 40% illustrated magazines. The deinking process must therefore be designed for this waste paper.
The method which is today preferred for newspaper deinking substance employs, in addition to various hydrocyclones used in the cleaning steps and screen sorting, and flotation, as shown by the first steps of FIG. 1. It is based on a method proposed for so-called SC papers, such as has already been discussed. It has been reported on also in the trade press. By this method, deinked pulps of a high degree of whiteness and good cleanness can be produced. Depending on the waste paper employed, it may, however, be that the cleanness is not sufficient for these high-grade printing papers, i.e. that the deinked waste paper may for example contain more dirt flecks than, for instance, the ground wood pulp used at the same time as fiber component.
Based on tests, a comparison between ground wood and a deinking pulp which was simultaneously bleached in the dispersing apparatus and then floated shows that while this pulp is good for the production of newsprint, it is not good for high-grade printing papers.
As a dispersing machine, there are customarily used disk disintegrating machines, particularly in order so to reduce the size of disturbing sticking substances and divide them up below the limit of visibility that they no longer disturb the paper production process.
For homogenizing of color particles, so-called single-shaft disintegrators are also known, particularly in processing plants for the production of board (Voith Reprint 2066; Wochenblatt fur Papierfabrikation, No. 23/24 (1977), 981-985).